A circuit of this type, which can be used for example in the horizontal deflection circuit of a television receiver, was proposed in our co-pending European patent application No. 79200687.6, not pre-published.
The synchronisation signal detector can establish the presence of the synchronising pulses by means of peak rectification; as a rule a time constant becomes effective here, e.g. through a change in the mean charging condition of a capacitor, so that the necessary switching can only take place after a certain time. Then phase synchronisation is usually necessary as well, as that the whole pull-in process takes a considerable time.
An object of the invention is to have the switching take place at the same time as the synchronisation without a disturbing delay, so that the synchronised state is reached instantaneously. This can e.g. be used for the synchronisation of the horizontal deflection in a television receiver. Particularly when a line frequency signal is used simultaneously for switching another stage, e.g. for the production of a supply voltage or for the high voltage generation, disturbing frequency variations, which may result in voltage fluctuations, can be largely avoided.